Control system for a waste wood burner

ABSTRACT

A control system for installation on existing waste burners at mill sites for the purpose of reducing emissions from the wood waste burned. A damper structure includes downwardly swingable doors positioned in response to the burner internal temperature. An under fire duct system supports combustion at the base of the waste pile while over fire blowers feed air about the perimeter of the pile in a cyclonic manner. Igniter units located about the burner shell retain burner temperature above a preset level by intermittent operation. Control means operates the systems components at preset temperatures to insure highly efficient combustion within the burner to reduce smoke and particulate emissions to a level acceptable to regulating authorities.

Stone et al.

May 1, 1973 CONTROL SYSTEM FOR A WASTE WOOD BURNER Primary Examinerl(enneth Wv Sprague [75] Inventors: Raymond E. Stone; Aubrey E. Wing, Atmmey james Gwnan f ld, both of Spring re Oreg ABSTRACT [73] Assignee: Industrial Construction Co., Ltd.,

A control system for installation on existing waste bur- Eugene, Oreg.

ners at mill sites for the purpose of reducing emissions [22] Filed: Feb- 28, 1972 from the wood waste burned. A damper structure in- [21] AppL No: 229,971 cludes downwardly swingable doors positioned in response to the burner internal temperature. An under fire duct system supports combustion at the base of U.S- Cl. R, C the waste over fire blowers feed air about o ..F23g the perimeter of the in a cyclonic mannen Igniter [58] Fleld of Search 10/ 7 18 18 C, units located about the burner shell retain burner tem- 110/18 E perature above a preset level by intermittent operation. Control means operates the systems components [56] References C'ted at preset temperatures to insure highly efficient com- UNITED STATES PATENTS hustion within the burner to reduce smoke and particulate emissions to a level acceptable to regulating 3,034,571 5/1962 Matthews ..1lO/l8 X authorities. 3,323,475 6/1967 Melgaard 3,538,865 10/1970 Lausmann ..1 [0/18 8 Claims, 10 Drawing Figures /8 6 3 3 r ,5 w lo a lo 1,. 1 a 8 -1 \v Patented May 1, 1973 5 Sheets-Sheet l Patented May 1, 1973 3,730,114

3 SheetsSheet 2 CONTROL SYSTEM FOR A WASTE WOOD BURNER BACKGROUND OF THE INVENTION The present invention relates to waste burners of the type commonly found in operation at a mill site for the burning of waste resulting from mill operations. The burner structure to which the present control system is applied typically is of conical shape ranging in height from approximately forty to sixty feet and of a like dimension across its base. These structures are sometimes termed wigwam burners by reason of their shape and vented dome for smoke exhaust. Such burners are normally fed by a conveyor discharging the wood waste to form a waste pile centrally within the structure. In the past the burner structure has simply served to confine the waste material while burning with emissions from the burner being largely unregulated. Wire screening at the upper end of the burner confined the larger burning particles to some extent with no effort being made to restrict visible smoke discharge or ash. More recently, because of the publics growing concern for air quality, attention has been given to the restricting of burner emissions with states and other governmental agencies enacting severe regulations for burner operation. Attention is now being directed toward restriction not only of particulate material and ash from the burners but also to smoke discharge which now must be below a certain level. In some states only a trace of smoke is permissible other than at burner start up.

To accomplish more complete burning, burners have been equipped with means for directing a cyclonic flow of air to facilitate fuel pile burning and simultaneously causing the settling of ash outwardly against the burner wall. Further, to promote efficient burning air ducting has been installed at the base of the burner to provide an upward air flow into the burning pile of waste. While such improvements have added to the burning efficiency of the burners they have not improved burner operation to the extent that their operation complies with regulations now in effect in most states. Mill operators faced with complying with the stringent regulations have had to resort, in some cases, to closing of their burners and have resorted to the costly trucking of waste wood to a dump site. Operation of a burner not operating in compliance with the pertinent regulations can incur severe fines with continued violation serving as a basis for judicial action against the mill owner or owners.

SUMMARY OF THE PRESENT INVENTION The instant invention is directed towards providing a system for regulating the burning rate of waste material within a burner, said system including air supply means, damper structure and an igniter system all systematically operable to achieve optimum burning.

The present burner control system envisions automatic control for the continuous regulation of a burner fire with the systems components working to sequentially ignite and control burning at a temperature that insures complete combustion with limited smoke emission from the burner. Installation of the present system is accomplished by modification of existing burner structures to render the operation of same in full compliance with the applicable state and federal regulations.

An important feature of the present system is the provision of oil fired igniters which are capable of rapidly igniting the waste pile and providing desired burner temperatures for efficient combustion of same. The igniters are disposed radially through the burner wall with the number of units used dependent upon the burner size. The novel waste igniter units permit the use of readily available, low cost furnace oil which is considered an advantage over other ignition units for such burners which utilize natural gas. The new fuel nozzle arrangement of the instant igniters, in conjunction with a forced air flow, provides a flame path of a desired length and pattern heretofore not possible.

Another important feature of the present control system concerns the damper door arrangement wherein damper doors move inwardly of the burner to direct its internal air flow. Accordingly, upwardly moving air within the burner is given a downward direction when the dampers are at least partially closed subjecting the air to being reheated by its flow past the burning fuel pile. At an elevated temperature, indicative of complete burning, the damper doors move towards an open position. The damper structure is regulated according to the burners internal temperature with damper door opening being initiated at approximately 950 with positioning of the dampers occurring at preset burner temperatures.

Operable in combination with the damper structure is an over fire system by which ambient air is forcefully directed onto the burning fuel pile. Similarly, an under fire system controls air to the base of the fuel pile as required to support efficient combustion.

In a typical start up operation the damper doors at the top of the burner are closed while simultaneously a blower of the under fire system is energized to provide an air flow to the base of the waste pile. When the collection of waste material is such as to cover the under fire air outlets the igniters are activated and remain on until such time as the burner temperature reaches 800 at which point the igniters are shut down while simultaneously over fire blowers are started.

At a temperature of 950 the damper doors initiate opening while the air flow from the under fire blower and igniter blower is greatly reduced. Normally, during burner operationthe temperature will recede below 900 at which time the damper doors will initiate closing. Dropping of burner temperature below 900 will jointly cause automatic operation of the damper doors along with full operation of the under fire system. For purposes of determining burner temperature the temperature probe is located approximately 3 feet below a damper door opening.

BRIEF DESCRIPTION OF THE DRAWINGS In the accompanying drawings:

FIG. 1 is a side elevational view of a burner structure modified with the present control system,

FIG. 2 is a sectional plan view taken along line 2--2 of FIG. 1,

FIG. 3 is a fragmentary plan view taken along line 3-3 of FIG. 1 showing details of the burner damper structure,

FIG. 4 is a sectional detail view taken along line 44 of FIG. 3,

FIG. 5 is a view similar to FIG. 4 taken along line 5- FIG. 6 is a side elevational view of a typical over fire blower assembly,

FIG. 7 is a side elevational view of a typical igniter unit,

FIG. 8 is a detail view of combustion chamber components within an igniter unit,

FIG. 9 is an end view of the right hand end of FIG. 8, and

FIG. 10 is a schematic diagram of the present systems circuitry.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With continuing reference to the accompanying drawings wherein applied reference numerals indicate parts similarly identified in the following specification, the reference numeral 1 indicates generally a burner structure of generally conical shape in place upon a base 2 and terminating upwardly in a domed portion indicated generally at 3.

Burners of the type used for burning mill waste are located adjacent the mill and fed by a conveyor at 4 which continuously delivers wood waste to form a waste pile WP within the burner. Such burners are fabricated with a sheet metal shell as at 5 to define a circular, open area in which the waste is piled several feet in height. The burning pile is continuously fed by conveyor carried wood waste which is burned very rapidly. Undesired smoke and particle emissions from the burner are a problem particularly during start up of the burner at the beginning of a work day as the pile of accumulated wood to be burned is of considerable size with oftimes a high moisture content.

Located along the interior wall surface of the burner shell is a temperature sensor in the form of a thermocouple 9 of the chromal-alumal wire type for the generation of an electrical current proportional to internal burner temperatures. The two thermocouple leads 9A-9B terminate remotely in a conventional strip chart recorder R (see FIG. which conventionally includes switch components actuable at preset burner temperatures for operation of later described relays of the present system. One such satisfactory strip chart recorder is that manufactured by the Honeywell Corporation, Industries Division, for temperature environments 0-l ,200 F. range.

DAMPER STRUCTURE Located immediately below the upper portion 3 of the burner is a damper door structure indicated generally at 6 which serves to provide a closure for the burner to prevent the escape of any smoke or particulate during burner start up and additionally to permit burner discharge only to periods above a specified burner temperature. With joint reference to FIGS. 1 and 3, it will be seen that the damper structure includes a pair of trusses 7 extending in a spaced apart manner across the burner top equidistant from the burner axis. The upper perimeter of the burner is reinforced for the support of the damper structure 6 by means of a burner ring 8 installed about the burner periphery below the damper structure.

A pair of damper doors at 10, as typically viewed in the plan view of FIG. 3, are of semi-circular shape and hingedly attached at 11 to inverted channel members 7A (FIG. 4) of each truss 7. With additional reference to FIGS. 4 and 5 it will be seen that the damper doors include stiffeners 10A. Arcuate sheet metal segments at 12, adjacent the burner ring and a closure plate 13 intermediate trusses 7, serve to fully close the upper end of the burner. Returning to FIG. 1, a door control arch at 14 comprises part of the damper structure and is supported by trusses 7 in an elevated, transverse manner. The arch serves primarily to suspend pulley means at 15 through which are reeved damper control cables 16 which pass downwardly around guides 17 to a powered cable drum later described. Control cable 16 is coiled about a powered drum 19 of a damper winch assembly indicated generally at 20 at the burner base. A motor 21, of the reversible type, is suitably geared for driving of winch 19 in opposite directions upon signals via later described circuitry. A limit switch 22 terminates motor operation to limit both unreeling and reeling in of cable 16 to control the downward and upward travel of the damper doors 10. The upper end of the burner structure supports a screen 18 of domed configuration which, prior to modification of the burner, was for the trapping of large burning particles.

UNDER FIRE SYSTEM For adequate supporting of combustion within the base of the waste pile WP a series of grate covered vents 25 are formed within the burner base 2 with each vent being in communication with ducting of the under fire system. This system is best viewed in FIG. 2 wherein an under fire blower of the centrifugal type is indicated at 26 discharging into a main duct 27 which extends downwardly and inwardly to the center of the burner below the base 2. A plenum is indicated at 28 for reception and dispersal of the air flow into secondary ducts 29 and ultimately to secondary plenums below each vent 25. The ducts 29 are of staggered lengths to evenly disperse the blower air upwardly into the waste pile. Blower 26, in a typical installation, will have a rating of 3600 CFM at seven and one-half inches static pressure. The grate covered vents 25 are substantially coplanar with the waste supporting surface of the burner base 2 with approximately four feet spacing therebetween. The air intake of blower 26 is provided with a damper 32 (FIG. 2) which is positioned through ninety degrees by an air cylinder 33 with a closed position permitting some air passage from the continuously running blower 26. A solenoid valve at 34 controls a flow of pressurized air into opposite ends of cylinder 33 for open and closing movement. The under fire system shown is the subject of a separate patent application of John F. Stutz and is described and shown herein only for purposes of a complete description.

OVER FIRE BLOWER SYSTEM Equispaced about the lower portion of the burner shell 5 are a series of centrifugal over fire blowers 35 each having a motor 36 as shown in FIGS. 1 and 2 with a complete blower shown in FIG. 6. Each blower mouth delivers air into a discharge duct 37 which is of welded plate construction with an intermediate section 37A serving to direct the air flow in a canted manner while the remaining portion progressively widens to restrict the air flow for discharge along an inclined slotlike opening 39. Duct 37 comprises two opposed halves which, by means of threaded fasteners 40 and slots formed in the opposite section, may be adjusted toward and away from one another to determine the width of opening 39 from one to three inches. The angularity of the discharge opening 39, with respect to the burner base 2 is approximately 40. Over fire blower air, so discharged, contributes to a cyclonic flow within the burner shell. Locating the blower so as to have an offset center line approximately sixty inches above the floor has been found highly satisfactory. The blower motors at 36 are automatically started upon the burner reaching an internal temperature of approximately 800. Switch means associated with the blower motors 36 permit their manual starting and stopping regardless of burner temperature. The automatic operation of both the blowers and the following described igniters is elaborated upon in the operation description.

IGNITER SYSTEM For igniting the waste pile within the burner a series of igniter units generally at 45 are spaced about the burner with each disposed so as to have a flame path extending directly into the pile to be burned. The present igniter structure constitutes an important part of the present invention as the flame path discharged by each igniter rapidly ignites the fuel pile to quickly achieve an internal burner temperature necessary for minimum burner emissions. The igniters are identical hence the following description of one is equally applicable to all.

With joint reference to FIGS. 1 and 2 and 7 through 9, a typical centrifugal fan assembly is indicated at 46 powered by an electric motor 47 with the fan discharging into an open ended cylindrical conduit 48 the latter extending radially into the burner shell 5. As best shown in FIGS. 7 9 each igniter unit includes a damper plate 49 positioned by an air cylinder 50 pivotally mounted at its base end above the fan housing. A solenoid valve 51 serves to direct pressurized air to either of the cylinder ends for actuation of piston rod 50A the latter pivotally linked to damper 49 via a lever arm 52. Damper plate 49 is positionable through an arc of 90 with the damper being of somewhat less area than the interior crossectional area of the fan mouth at 46A to permit an air flow from continuously operating motor 47 through mouth 46A even when damper 49 is in a transverse, closed" position. Downstream from the fan mouth is an adapter section 53 squared at one end and circular at its downstream end for registration with the end of conduit 48. Fan assembly 46, in one satisfactory embodiment, is rated at 1,000 CFM; 6 inch static pressure and is powered by a 2 HP. motor.

Conduit 48, outwardly of the burner shell 5, receives a pair of shielded ignition wires 54, with each wire terminating in contact with a metal rod constituting ignition leads 57. Similarly an oil supply line 55 also enters conduit 48 with both oil line 55 and ignition leads 57 being supported interiorly of the conduit at intervals by stand-off elements as at 56 with ceramic insulators as at 56A isolating each lead 57 from other metal components. A solenoid operated oil valve at 59 controls the flow of oil from a pressurized source.

Located adjacent the inner end of igniter conduit 48 and coaxial therewith is an ignition chamber in the form of an open sleeve 58 retained in place in the conduit by means of spacer elements 60. Located within sleeve 58 is a combination deflector and stand-off at 61 having fan-like radiating projections causing the air flow through the sleeve to be partially restricted while also imparting fuel mixing turbulence to the ignition chamber air flow. One suitable igniter unit includes a conduit 48 of 8 inch diameter while sleeve 58 is of 4 inch diameter.

Important to the present invention are details of the fuel nozzle arrangement which includes a pair of spaced apart nozzles 62-63 in sleeve 58 each having a triangular spray pattern in perpendicular relationship to each other. The fuel nozzles are advantageously spaced approximately one and one-quarter inches apart with an elbow 64 providing a branched fuel flow to nozzle 63 and each discharging a fan shaped fuel pattern as seen in broken lines of FIGS. 8 and 9. The nozzles provide an adequate fuel flow for the production of 8 million B.T.U.s at maximum igniter operation with fuel pressurized to PSI.

For arc ignition the metallic rods 57 terminate forwardly in downwardly inclined electrodes 57A with electrode tips spaced apart approximately three sixteenths of an inch and located within the spray pattern of at least one nozzle. Insulators at 65, retained by the combination deflector and stand-off 61, insulate and position the electrode tips in the desired position. A transformer 66 for each igniter provides adequate voltage, approximately 10,000 volts, for continuous arcing between the electrode tips during igniter operation. The ignited fuel-air mixture is carried to the waste pile by the unrestricted air flow exteriorly of sleeve 58. As will become clear in the following description, during automatic operation of the present system all of the igniters will function simultaneously at any time burner temperature is below 800 F.,.

ELECTRICAL SYSTEM With reference to the electrical system shown in the schematic block diagram in FIG. 10, the Honeywell recorder, indicated at R, conventionally includes a plurality of cam actuated micro switches actuated in response to preset burner temperatures sensed by thermocouple 9 via leads 9A-9B. Each of said micro switches is in a separate control circuit for relays indicated at R-l, R-2, R-3 and R-4 with relays being located within a control panel CP in FIG. 10. Accordingly, an electromotive force from thermocouple 9 is translated into a continuous chart recording by the recorder scribe while additionally serving to actuate internal micro switches in the well known manner for the operation of relays R-l through R-4. An electrical source for the recorder is indicated at S-2.

The operation of the present system will be described jointly with a description of the electrical system as follows. The control panel is provided with a I20 volt AC source at S-l with a master control switch at 71 closeable to energize a main conductor 70, system operating light 73 and the under fire blower motor 30. Also energized upon closure of master switch 71 are each of the four igniter unit fan motors 47.

A first single pole, double throw switch at 74 is positionable to automatic or manual with the former applying current to one side of relay R-l. A control circuit for relay R-l includes a recorder actuated micro switch (not shown) and a lead 75. Below 800 a first set of contacts in R-l are closed to apply current to an igniter on light 76, a motor 77 for driving a fuel oil pressurizing pump, the primary of each transformer 66, solenoid oil control valves 59 and igniter unit damper controlling air valve solenoids 51. Accordingly, each igniter is put into operation remaining on until such time as said first set of contacts in R-l open in response to a burner temperature exceeding 800. The manual position of switch 74 permits momentary igniter operation above 800 which, for example, may be used in the igniting of a waste pile having a high moisture content.

A second single pole, double throw switch at 80 includes automatic and manual positions with the former applying current remaining set of contacts in relay R-l (represented by a second block identified by R-l). Said remaining set of contacts of R-l are closed by said control circuit lead 75 upon the burner temperature reaching 800 simultaneously with said first set of relay contacts opening to terminate igniter operation. The second or remaining contacts in relay R-l upon closing start operation of the blower motors 36 of the blower system as indicated by a blower operating light 81 being on. The manual position permits blower operation at temperatures below 800 during starting if deemed advantageous in certain cases.

Relay R-2 includes a normally closed set of contacts which open at 900 upon a control circuit being established via a control lead 82 in circuit with a recorder micro switch not shown. Said set of relay contacts are in series with a limit switch 22A and with that winding of damper control motor 21 associated with powering of the damper doors to a closed position. The damper doors 10, at this point in the burner operation, remain closed in their starting position. Also energized at 900 by the opening of relay contacts in relay R-Z is solenoid valve 34 controlling the air cylinder 33 to close the damper 32 of the under fire blower 26.

Relay R-3 includes contacts in series with a limit switch 228 in switch housing 22 and with that winding of damper control motor associated with opening of damper doors 10. A control lead 83 from a recorder actuated micro switch serves to actuate relay R-3 upon a temperature of 950 being sensed by thermocouple 9 to close relay contacts in R-3 to drive motor 21 in a damper door opening direction. In actual operation the travel of doors 10 will be reversed prior to the opening of limit switch 22 B by reason of the burner temperature receding to 900 at which time R-2 will close its contacts to drive motor 21 in an opposite or door closing direction. A seventeen FPM linear speed of cable 16 during reeling and unreeling has been found satisfactory.

Relay R-4 closes upon recorder lead 84 being energized in response to a maximum acceptable temperature within the burner, for example, 1,l50. The relay R-4 may be wired around master switch 71 to the source to enable operation of a warning device 85 at all times.

During initial operation of the igniters during burner start up the igniter blowers 46 cause an extended flame path of several feet to project against the waste pile while simultaneously air is directed to the pile base by the under fire system. Rapid bringing of the burner temperature to 800 degrees while keeping of the damper doors it) closed prevents objectionable burner emissions. At 800 degrees the over fire blowers 35 start operation to impart a cyclonic circulation to air within the burner to adequately ventilate the burning waste pile. Steam is removed from about the pile and fly ash is deposited about the interior perimeter of the burner shell 5. At 900 the under fire system damper is closed with the burning now being supported by restricted air flow from the under fire system (blower 26 remaining in operation) and the output of the continuously centrifugal blowers 46 of each igniter unit. The dampers of both blower 26 and centrifugal fans 46 permitting such reduced air flows.

Upon 950 being reached the damper doors 10 start downward movement towards an open position which advantageously causes deflection of internal burner air currents downwardly for circulation past the burning waste pile to insure complete combustion of airborne burning particles.

While the foregoing description has been rendered with regard to but a typical burner installation of the present system it is not intended to restrict the scope of the protection sought as obviously various changes will be readily apparent to those skilled in the art to suit specific installations with such changes coming within the scope of the invention as set forth in the appended claims.

What we desire to secure under a United States Letters Patent is:

1. A system for regulating the burning of material within a waste wood burner structure to minimize smoke and particulate emissions therefrom, said system comprising,

a damper structure closing the upper end of the burner and including damper doors mounted for downward opening movement, door positioning means operable to open and close said doors in response to internal burner temperatures,

an under fire system comprising a blower, a multitude of vents discharging air from said blower into the bottom of a waste fuel pile,

over fire blowers disposed about the periphery of the burner for imparting a cyclonic flow to air within the burner,

igniter units spaced about the burner, each of said igniter units comprising,

a conduit extending inwardly of the burner structure, a source of pressurized air at the outer end of said conduit, an ignition chamber within said conduit adjacent its discharge end, said chamber embodying electrodes in circuit with an electrical source for spark ignition, fuel nozzles discharging fan shaped spray patterns arranged so as to intersect each other, and

signal producing means including a signal input component responsive to the temperature within the burner, said last mentioned means adapted to control igniter operation terminating same at a preset temperature and initiating over fire blower operation at an elevated temperature, said signal producing means additionally controlling the operation of the door positioning means to open the damper doors upon internal burner temperature reaching a preset temperature level, at which level the discharge from the burner is devoid of objectionable smoke and particulate contaminants.

2. The system as claimed in claim 1 wherein said source of pressurized air for each igniter unit is a continuously operating centrifugal fan, a damper disposed intermediate the fan and the conduit and at all times permitting at least partial fan discharge through said conduit for joint cooling of the conduit and fire ventilation.

3. The system as claimed in claim 2 wherein said igniter units and said over fire blowers are sequentially operated with igniter operation terminating and blower operation commencing at approximately 800 F.,.

4. The system as claimed in claim 2 wherein said ignition chamber further includes a sleeve coaxially disposed within said igniter conduit, means within said sleeve for supporting said fuel nozzles and electrodes, said means additionally imparting a rotational direction to air passing through said sleeve for fuel-air mixing purposes.

5. The system as claimed in claim 1 wherein said signal producing means comprises a temperature recorder embodying switch components, said switch components closeable in response to burner temperatures and comprising part of plural relay control circuits,

a control panel including relays actuated by said control circuits, said door positioning means, over fire blowers and igniter units having electrical components in circuit with said relays for automatic operation to regulate internal burner temperature within a desired range, manually positionable switch means in said control panel for bypassing those relays in circuit with said over fire blowers and said igniter units to permit operator control of same.

6. An oil fired igniter unit for use in igniting waste wood in a burner enclosure, said igniter unit comprismg,

an elongate conduit having a discharge end located interiorly of the burner enclosure adjacent a waste pile therein,

fan means associated with the opposite end of the conduit exteriorly of the burner enclosure,

damper means remotely controlled for regulating the air flow, and

an ignition chamber located within the conduit down-stream from the damper means and comprising,

a sleeve coaxially disposed within said conduit adjacent the conduits discharge end,

means partially restricting air flow through said sleeve while imparting turbulence to the sleeve air flow,

fuel nozzles within said sleeve having fan shaped spray patterns intersecting each other,

electrodes located within said sleeve providing a spark gap the latter disposed within the spray pattern of at least one fuel nozzle.

7. The oil fired igniter unit as claimed in claim 6 wherein said restricting means is of fan-like configura- The oil fired igniter unit as claimed in claim 7 wherein said restricting means additionally serves to support said fuel nozzles and electrodes within said sleeve. 

1. A system for regulating the burning of material within a waste wood burner structure to minimize smoke and particulate emissions therefrom, said system comprising, a damper structure closing the upper end of the burner and including damper doors mounted for downward opening movement, door positioning means operable to open and close said doors in response to internal burner temperatures, an under fire system comprising a blower, a multitude of vents discharging air from said blower into the bottom of a waste fuel pile, over fire blowers disposed about the periphery of the burner for imparting a cyclonic flow to air within the burner, igniter units spaced about the burner, each of said igniter units comprising, a conduit extending inwardly of the burner structure, a source of pressurized air at the outer end of said conduit, an ignition chamber within said conduit adjacent its discharge end, said chamber embodying electrodes in circuit with an electrical source for spark ignition, fuel nozzles discharging fan shaped spray patterns arranged so as to intersect each other, and signal producing means including a signal input component responsive to the temperature within the burner, said last mentioned means adapted to control igniter operation terminating same at a preset temperature and initiating over fire blower operation at an elevated temperature, said signal producing means additionally controlling the operation of the door positioning means to open the damper doors upon internal burner temperature reaching a preset temperature level, at which level the discharge from the burner is devoid of objectionable smoke and particulate contaminants.
 2. The system as claimed in claim 1 wherein said source of pressurized air for each igniter unit is a continuously operating centrifugal fan, a damper disposed intermediate the Fan and the conduit and at all times permitting at least partial fan discharge through said conduit for joint cooling of the conduit and fire ventilation.
 3. The system as claimed in claim 2 wherein said igniter units and said over fire blowers are sequentially operated with igniter operation terminating and blower operation commencing at approximately 800* F.,.
 4. The system as claimed in claim 2 wherein said ignition chamber further includes a sleeve coaxially disposed within said igniter conduit, means within said sleeve for supporting said fuel nozzles and electrodes, said means additionally imparting a rotational direction to air passing through said sleeve for fuel-air mixing purposes.
 5. The system as claimed in claim 1 wherein said signal producing means comprises a temperature recorder embodying switch components, said switch components closeable in response to burner temperatures and comprising part of plural relay control circuits, a control panel including relays actuated by said control circuits, said door positioning means, over fire blowers and igniter units having electrical components in circuit with said relays for automatic operation to regulate internal burner temperature within a desired range, manually positionable switch means in said control panel for bypassing those relays in circuit with said over fire blowers and said igniter units to permit operator control of same.
 6. An oil fired igniter unit for use in igniting waste wood in a burner enclosure, said igniter unit comprising, an elongate conduit having a discharge end located interiorly of the burner enclosure adjacent a waste pile therein, fan means associated with the opposite end of the conduit exteriorly of the burner enclosure, damper means remotely controlled for regulating the air flow, and an ignition chamber located within the conduit down-stream from the damper means and comprising, a sleeve coaxially disposed within said conduit adjacent the conduits discharge end, means partially restricting air flow through said sleeve while imparting turbulence to the sleeve air flow, fuel nozzles within said sleeve having fan shaped spray patterns intersecting each other, electrodes located within said sleeve providing a spark gap the latter disposed within the spray pattern of at least one fuel nozzle.
 7. The oil fired igniter unit as claimed in claim 6 wherein said restricting means is of fan-like configuration.
 8. The oil fired igniter unit as claimed in claim 7 wherein said restricting means additionally serves to support said fuel nozzles and electrodes within said sleeve. 